It is proposed to purchase a complete state-of-the-art ultrasensitive microcalorimetry system for the University of Illinois at Chicago (UIC), to be used for the study of protein-ligand interactions and protein domain organization and stability. The equipment consists of an ultrasensitive isothermal titration calorimetry (ITC) unit and an ultrasensitive differential scanning calorimetry (DSC) unit. The DSC unit will replace a much older unit that has only one hundredth the sensitivity of the replacement, while the ITC unit represents a new capability that is not presently available at the university. Both components represent the latest technology in ultrasensitive calorimeters, with sensitivities and baseline stabilities greatly improved over the previous generation. This will allow critical questions to be answered that can not currently be addressed for lack of appropriate instrumentation or sufficient material. This in turn will greatly enhance the significance and competitiveness of the research that will make use of the instrumentation. Since isothermal titration calorimetry provides, in a single titration, both deltaH and deltaG values, and hence deltaS as well, it gives a complete thermodynamic analysis of binding and is therefore greatly superior and more direct than any other approach. DSC provides information on protein stability, domain organization and heat capacity in native and unfolded states. Four NIH-funded research groups at UIC will be the primary users of the equipment and will together use 80-90% of available time. These are Drs. Gettins and Liao in the College of Medicine and Drs. Olson and Patston in the College of Dentistry. Remaining time will be available to all other investigators, with preference given to NIH-funded researchers at this institution. Systems that will be examined by ITC or DSC include (i) The binding of ligands, including the chaperone protein RAP, to the LDL receptor-related protein (LRP), (ii) calcium binding to ligand-binding domains of LRP, (iii) binding of beta-amyloid peptide to alpha2-macroglobulin, (iv) domain-domain interactions in LRP and in LRP-protein ligand complexes, (v) stability of LRP domains in the absence and presence of calcium, (vi) heparin binding to antithrombin variants, (vii) interaction of antithrombin and other serpins with target proteinases, (viii) stability of native and cleaved serpins, (viii) binding of hormone to thyroxine binding globulin, (ix) DNA binding to winged helix transcription factors, (x) protein-protein interactions involving Ubll.